Wholly aromatic polyester resins long have been known. For instance, p-hydroxybenzoic acid homopolymer and copolymers have been provided in the past and are commercially available. Those wholly aromatic polyesters normally encountered in the prior art have tended to be somewhat intractable in nature and to present substantial difficulties if one attempts to melt process the same while employing conventional melt processing procedures. Such polymers commonly are crystalline in nature, relatively high melting or possess a decomposition temperature which is below the melting point, and when molten frequently exhibit an isotropic melt phase. Molding techniques such as compression molding or sintering may be utilized with such materials; however, injection molding, melt spinning, etc. commonly have not been viable alternatives or when attempted commonly have been accomplished with difficulty.
Representative publications which discuss wholly aromatic polyesters include: (a) Polyesters of Hydroxybenzoic Acids, by Russell Gilkey and John R. Caldwell, J. of Applied Polymer Sci., Vol. II, Pages 198 to 202 (1959), (b) Polyarylates (Polyesters From Aromatic Dicarboxylic Acids and Bisphenols), by G. Bier, Polymer, Vol. 15, Pages 527 to 535 (August 1974), (c) Aromatic Polyester Plastics, by S. G. Cottis, Modern Plastics, Pages 62 to 63 (July 1975), and (d) Poly(p-Oxybenzoyl Systems): Homopolymer for Coatings: Copolymers for Compression and Injection Molding, by Roger S. Storm and Steve G. Cottis, Coatings Plast. Preprint, Vol. 34, No. 1, Pages 194 to 197 (April 1974). See also, U.S. Pat. Nos. 3,039,994; 3,169,121; 3,321,437; 3,553,167; 3,637,595; 3,651,014; 3,723,388; 3,759,870; 3,767,621; 3,787,370; 3,790,528; 3,829,406; and 3,890,256.
Also, it more recently has been disclosed that certain polyesters may be formed which exhibit melt anisotropy. See for instance, (a) Polyester X7G-A Self Reinforced Thermoplastic, by W. J. Jackson Jr., H. F. Kuhfuss, and T. F. Gray, Jr., 30th Anniversary Technical Conference, 1975 Reinforced Plastics/Composites Institute. The Society of the Plastics Industry, Inc., Section 17-D, Pages 1 to 4, (b) Belgian Pat. Nos. 828,935 and 828,936, (c) Dutch Pat. No. 7505551, (d) West German Pat. Nos. 2520819 and 2520820, (e) Japanese Pat. No. 43-223.
It is an object of the present invention to provide an improved melt processable wholly aromatic polyester which is free of ring substitution.
It is an object of the present invention to provide an improved melt processable aromatic polyester capable of forming a thermotropic melt phase at a temperature below approximately 425.degree. C., preferably below approximately 330.degree. C., even in the absence of ring substitution.
It is an object of the present invention to provide an improved wholly aromatic polyester which exhibits a melting point well below its decomposition temperature.
It is an object of the present invention to provide an improved wholly aromatic polyester which is crystalline in nature and highly tractable.
It is an object of the present invention to provide an improved wholly aromatic polyester which readily may be injection molded to form a molded article exhibiting superior tensile strength, flex strength and impact strength.
These and other objects, as well as the scope, nature and utilization of the invention will be apparent from the following detailed description.
In commonly assigned U.S. Pat. No. 686,191 filed concurrently herewith and now abandoned, by Gordon W. Calundann, Herbert L. Davis, Frederick J. Gorman, and Robert M. Mininni, entitled "Improved Melt Processable Thermotropic Wholly Aromatic Polyester Which Is Particularly Suited for Fiber Formation" is specifically claimed a species of the generic invention defined herein which is free of ring substitution and wherein an isophthaloyl moiety and/or meta-dioxy phenyl moiety recur in the wholly aromatic polyester in addition to p-oxybenzoyl moiety, 2,6-dicarboxynaphthalene moiety, and symmetrical dioxy aryl moiety.